ThreeBallot

ThreeBallot is a voting protocol invented by Ron Rivest and Warren D. Smith in 2006. ThreeBallot is an end-to-end (E2E) auditable voting system that can in principle be implemented on paper. The goal in its design was to provide some of the benefits of a cryptographic voting system without using cryptographic keys. It may be difficult for a vote to be both verifiable and anonymous. ThreeBallot attempts to solve this problem by giving each voter three ballots: one verifiable, and two anonymous. The voter chooses which ballot is verifiable and keeps this secret; since the vote-counter does not know, there is a 1/3 chance of being discovered destroying or altering any single ballot. The voter is forced to make two of their three ballots cancel each other out, so that they can only vote once.

ThreeBallot is a voting protocol invented by Ron Rivest and Warren D. Smith in 2006. ThreeBallot is an end-to-end (E2E) auditable voting system that can in principle be implemented on paper. The goal in its design was to provide some of the benefits of a cryptographic voting system without using cryptographic keys. It may be difficult for a vote to be both verifiable and anonymous. ThreeBallot attempts to solve this problem by giving each voter three ballots: one verifiable, and two anonymous. The voter chooses which ballot is verifiable and keeps this secret; since the vote-counter does not know, there is a 1/3 chance of being discovered destroying or altering any single ballot. The voter is forced to make two of their three ballots cancel each other out, so that they can only vote once.

Broken encryption

The encryption system used in the ThreeBallot was broken by a correlation attack devised by Charlie Strauss, who also showed how it could be used to prove how you voted. While the ThreeBallot is secure if there is only one yes/no question on the ballot, Strauss observed that it is not secure when there are multiple questions, including the case of a single race with many candidates from which to choose. His attack exploited the fact that not every combination of 3 ballots forms a valid triple: proposed triples with 3 or 0 votes cast in any row on the ballot (not just one race of interest) can be rejected, since those ballots could not be from the same voter. Likewise, proposed trines resulting in a vote for more than one candidate in any race can be rejected. Since there are exponentially more possible vote patterns than there are ballots cast in a typical precinct (or even people in the world), statistically most of the ballots cast can be trined uniquely for sufficiently long ballots. Typically, 90% of ballots can be reconstructed on ballots with just 11 to 17 questions. This likely allows a voter's votes to be known by anyone with the receipt. Moreover, even without a receipt, it leaks information that could discredit a voter's claimed candidate selections. Consequently, a voter conspiring to prove their vote (for money, coercion, or posterity) could mark all the ballots in a previously agreed unusual pattern that could later prove to a third party whether the agreement was kept (even without seeing the receipt). In either case, the veil of the secret ballot is pierced and traceable to the ID number on the receipt.

Revised ThreeBallot

Rivest later acknowledged this logic error in the original concept and revised the RFC schema in his final publication to require tearing off each row (each yes/no) individually (destroying the correlation of the questions) and also having unique tracking numbers on each mark on each ballot (not just one ID for each column ballot). While this did restore the unbreakable aspect of the scheme, the proliferation of receipts (one per row) and chopped ballots rendered the mechanics of processing the votes or for a voter reviewing a receipt significantly complex, thus undermining its intended simplicity. An electronic version addressing the paper-ballot implementation and usability problems was proposed by Costa, et al.

See also

Electoral fraud

References

Text derived from https://en.wikipedia.org/w/index.php?oldid=1330281180 under CC BY-SA 4.0; modifications have been made.